Final answer:
The choroid is characterized by the presence of many melanocytes, making option (D) the correct choice. It is part of the vascular tunic and helps provide a blood supply to the eyeball, while also containing pigment cells that absorb light.
Step-by-step explanation:
The correct answer to the question regarding the characteristic of the choroid is (D) It contains many melanocytes. The choroid is indeed highly vascular tissue; it is not avascular. This vascular tissue is found in the wall of the eye, and it helps supply the outer retina with blood.
It is not correct that the choroid is the posterior portion of the tunica fibrosa; rather, it is part of the vascular tunic, which is the middle layer of the eye. Also, the choroid is not tightly attached to the sclera. Instead, parts of the vascular tunic, including the choroid, the ciliary body, and the iris, are loosely attached to the fibrous tunic, allowing for necessary adjustments in the eye's focus.
Another important structure within the eye is the ciliary body, which is a smooth muscle structure on the interior surface of the iris. The ciliary body controls the shape of the lens with the help of zonule fibers and provides support for the lens. Additionally, the choroid is heavily pigmented with melanocytes, which helps absorb excess light and prevents it from scattering within the eye.